Transport devices are frequently driven directly by linear motors. In this case, it is necessary to transmit power and information to the driven components in order in turn to be able to carry out specific functions there, such as loading and unloading, and to supply devices for this purpose.
Problems relating to such devices, especially with linear motors, will be explained in the following text using an example. A piece goods transport device includes a large number of vehicles which themselves carry various goods, such as packages, postal items etc. The vehicles move on predetermined paths, such as rails or the like, and are driven by one or more linear motors (LIM).
One or more stators of these linear motors (LIM) is or are fitted in a fixed position or positions between the rails. The secondary parts of the linear motors (LIM) are attached to the vehicle to be driven and, by way of example in the case of an asynchronous three-phase LIM in the simplest case, include a solid conductor, for example aluminum or copper, but are often also equipped with a laminated core behind this solid conductor in order to improve the magnetic return path. When the vehicle with the secondary part of the linear motor (LIM) moves over the fixed stator a driving force acts on the vehicle as a result of the LIM principle, which is known per se. Since the vehicles are coupled to one another, even vehicles which are not being driven at any given time and are accordingly located between two stators are driven.
By way of example, in order to sort packages, the vehicles have to pick up and deposit piece goods in order that the transport device can carry out its correct task. For this purpose, the trucks have a conveyor device, for example a conveyor belt with an electrical drive or the like, which can pick up and place down the piece goods at specific points transversely with respect to the movement direction of the vehicle. On the one hand, power is required for this drive located on the vehicle. On the other hand, it is necessary to signal in some suitable manner to the drive when and in what way piece goods should be picked up or placed down. Furthermore, it may be necessary to transmit information from the vehicle about the piece goods, for example the weight, size, shape, code read from the piece goods, etc., to a fixed controller for the transport device.
It is known from the prior art, for moving parts of a transport device to be supplied with electrical power and for the communication with such moving parts to be organized via sliding contacts as well as sliding contact lines fitted to the movement path. Both the sliding contacts and the sliding contact lines are subject to a certain amount of wear.
Accordingly, both the sliding contacts and the sliding contact lines require intensive maintenance. Furthermore, the sliding contact lines and the sliding contacts make up a considerable proportion of the total costs of the transport device.
One example of the need to transmit power and information to rotating components is that for measurements directly on rotating structural parts. This is the situation, for example, for torque determination, in which strain gauges are used to determine the torsion on the shaft resulting from the torque. On the one hand, the rotating measurement device and signal processing require power, while on the other hand the measured value must be transmitted to the fixed part of the system. Further examples occur with the operation of magnetic bearings or the control of rotating field windings.
According to the prior art, power and data are transmitted to rotating structural parts via slip-rings with associated sliding contacts. This is associated with the disadvantages which have already been mentioned further above. In particular for data transmission to rotating components, telemetry devices are known, although these are corresponding costly.
U.S. Pat. No. 6,326,713 B1 discloses an electrical machine and a method for transmission of power between the different systems, in particular the stator and the rotor of the machine, in which power is transmitted inductively. The electrical machine is modified for this purpose, and special coils with suitable inductances are provided. Furthermore, DE 199 32 504 A1 describes the provision of non-contacting power and data transmission between two parts which can rotate with respect to one another, with the transmission path for power and data transmission comprising two or more coils which are mounted such that they can rotate with respect to one another. For power transmission in the medium-frequency range from a primary stationary conductor to moving secondary loads, DE 42 36 340 A1 provides for the secondary conductors to have coils which are rotated about the primary energy producer with a coil. The same principle of inductive power transmission from one coil to another coil is disclosed in WO 01/88931 A1.
Furthermore, U.S. Pat. No. 5,521,444 A discloses a device for transmission of electrical power from a stationary device element to a rotating device element, without any direct contact.